1. Field of the Invention
This invention relates to catalyst compositions for curing polymeric coatings. More particularly this invention relates to compositions for catalyzing the curing of polymer compositions containing hydroxyl and isocyanate groups.
The solvent resistance of organic polymer coatings can be substantially increased by "curing" or "crosslinking". During this process chemical bonds are formed between polymer molecules. One method for curing involves reacting a polymer containing pendant functional groups with a compond containing two or more groups that will react with the functional groups on the polymer.
A specific method for curing polymer compositions is to react a polymer containing pendant hydroxyl groups with a blocked polyfunctional isocyanate. Alternatively, both hydroxyl and blocked isocyanate groups can be present on the same polymer. An isocyanate group can be blocked by reacting it with an active hydrogen-containing compound such as an alcohol or phenol. When a polymer composition containing hydroxyl and blocked isocyanate groups is heated to above 100.degree. C. the blocking reaction reverses, freeing the isocyanate groups which then react with the hydroxyl groups to form a cross-linked structure.